Liquid-Infused Membranes Exhibit Stable Flux and Fouling Resistance

Abstract

Antifouling membranes that offer excellent operational lifetimes are critical technologies needed to meet the growing demand for clean water. In this study, we demonstrate antifouling membranes featuring an ultrathin oil layer that stayed immobilized on the surface and in the pore walls of poly­(vinylidene fluoride) membranes for multiple cycles of operation at industrially relevant transmembrane pressures. An optimized quantity of a commercial Krytox oil with either a low (K103) or a high viscosity (K107) was infused onto the active surface and into the pores of membranes with a 0.45 μm pore size. The presence of the oil layer was qualitatively confirmed using crystal violet staining and variable pressure scanning electron microscopy. Using a dead-end stirred cell, a consistent pure water permeance value of 3000 L m–2 h–1 bar–1 was achieved for the K103 liquid-infused membranes for at least 10 operation cycles, which was expectedly lower than the permeance of bare control membranes (∼16 000 L m–2 h–1 bar–1), suggesting that a stable oil layer was formed on all membrane-active sites. To quantify if oil was lost during membrane operation, extensive thermogravimetric analysis was conducted on both the as-prepared and used membranes. When challenged with the microorganism, Escherichia coli K12, the liquid-infused membranes statistically reduced microbial attachment by ∼50% versus the control membranes. For the first time, we have demonstrated that by forming an immobilized, robust, and stable oil-coated membrane, we can generate high-performance membranes with stable permeance values that can be operated at relevant transmembrane pressures and provide long-lasting antifouling properties.

Improved Recovery of Captured Airborne Bacteria and Viruses with Liquid-Coated Air Filters

“…23,34 However, recent work has shown that even imperfectly matched liquid− substrate pairs can create functional, stable liquid coatings under flow conditions. 40 The imperfectly matched polypropylene of the HEPA membrane and the PFPE liquid used in this system may therefore be creating a coating layer that is stable enough for filtration but unstable enough to be easily removed.…”

“…Over the past decade, immiscible liquid coatings on solid surfaces, otherwise known as liquid-infused surfaces, have demonstrated their strong potential for the handling and manipulation of biological samples, including bacteria, − proteins, and biological fluids, both in vitro and in vivo. − These systems consist of a material substrate and an infusing liquid, associated via chemical affinity, to repel immiscible liquids. , Recently, the approach of adding an immobilized liquid layer to a solid substrate has also been applied to filtration materials to produce either liquid-gated membranes, in which the liquid reversibly fills the pores, − or liquid-coated membranes, in which the pores remain open . Most of these studies have used commercial polytetrafluoroethylene (PTFE) filters that were coated with a perfluoropolyether (PFPE) oil. ,, Liquid-coated filters have primarily been studied as a filter for multiphase separations, ,, preventing fouling of inorganic matter, , increasing flux recovery against organic foulants, and improving the durability of filters for water treatment .…”

Improved recovery of captured airborne bacteria and viruses with liquid-coated air filters

“…30,41 However, recent work has shown that even imperfectly-matched liquid-substrate pairs can create functional, stable liquid coatings under flow conditions. 47 The imperfectly matched polypropylene of the HEPA membrane and the PFPE liquid used in this system may therefore be creating a coating layer that is stable enough for filtration, but unstable enough to be easily removed.…”

“…In contrast, if the PFPE liquid coating was easily displaced by the CV solution, we anticipated seeing a deeply stained filter. 47 Figure 6A shows the results of the staining tests on the PTFE-, HEPA-and CNFM-LNs compared to dry controls. No staining was observed on either the PTFE dry controls or PTFE-LNs, in agreement with their known anti-fouling nature.…”

“…41,42 Recently, liquid coatings have been applied to filtration materials to produce either liquid-gated membranes, in which the liquid reversibly fills the pores, [43][44][45][46] or liquid-coated membranes, in which the pores remain open. 47 Most of these studies have used commercial polytetrafluoroethylene (PTFE) filters that were coated with a perfluoropolyether (PFPE) oil; 43,46,48,49 although others have used elastomers, 50 polyvinylidene fluoride (PVDF) filters, 45,47,51,52 functionalized polyethylene terephthalate (PET), 53 and electrochemical surface modifications to stainless steel. 44 Liquid-coated filters have primarily been studied as a filter for multiphase separations, 44,46,50 separating emulsions, 53 preventing fouling of inorganic matter, 44,48 increasing flux recovery against organic foulants, 19 and improving the durability of filters for water treatment.…”